(Note: This is sorta like a parallel to my unanswered thread on a hypothetical alien cellular structure for a sci-fi novel series I'm in the prosses of creating. You can find it here.)

Because DNA and, I assume, RNA is so incredibly complex, I'd figure it highly unlikely for it to develop on a seperate planet. So, what other substances, even if hypothetical or non-existant, could possibly be substituted for DNA and RNA in alien life forms?